It has long been known that the rays of the sun can be utilized to illuminate and heat the interior of a building. For this purpose, sky lights and windows are often provided. However, there are certain instances when the rays of the sun are too strong and it is therefore desired to prevent the direct rays from entering the building and to permit only indirect rays to enter to give the desired illumination without the attendant heat. A number of structures have been devised to give this desired result.
Large halls in factories, storehouses, etc., where good illumination without much heating is desired are frequently provided with so-called "saw-roof" structures. These are roofs which are formed by modular triangles which provide windows or openings which are generally directed toward the north in the northern hemisphere (south in the southern hemisphere).
Corrugated asbestos cement roofs can be provided with "Northor" elements, which project out of the surface of the roof and which are provided with a transparent wall facing the northern direction.
Devices of this nature admit only those light rays coming from one direction. They cannot and do not take into account the time of day or the time of year, both of which affect the strength of the incident rays.
In conventional protective glass, the glass is tinted or a metallic coating is layered on the glass. However, this sort of protective glass has two major disadvantages. First, the tint or metallic coating itself absorbs light and converts it into heat which is radiated inside the building. Second, the tint filters out a large portion of the light which greatly decreases the illumination within.
It has been suggested that complementary panels comprising on one side thereof prisms of uniform dimensions might be used to selectively transmit light while eliminating glare. For example, U.S. Pat. No. 3,393,034 and U.S. Pat. No. 3,603,670 each show the use of such panels or plates wherein one surface of each prism is frosted or opaque or has a reflective coating. Such panels, in addition to suffering from the defects discussed above of tinted glass, are also technically very difficult and costly to manufacture.
It has also been suggested in U.S. Pat. No. 3,438,699 to utilize an adjustable multiple slat assembly, i.e. a venetian blind, having slats which can be manually rotated as desired, each slat comprising at least two transparent pieces having intermeshing prisms. These prisms have angles of 90.degree..times.45.degree..times.45.degree. in order to provide a totally reflective zone substantially only at 90.degree.. This assembly requires constant manual adjustment during use to maintain the slat at an angle of 90.degree. with respect to the impinging sunlight and is applicable only to planar slats.